The Devils Chimney breccia pipe, Dyamberin area, northeastern New South Wales.
Titel:
The Devils Chimney breccia pipe, Dyamberin area, northeastern New South Wales.
Auteur:
Egan, M. J. Ashley, P. M.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 39 (1992) nr. 2 pagina's 239-247
Jaar:
1992-05
Inhoud:
The Devils Chimney breccia pipe is heterolithic and was forcefully emplaced as a subvertical body into the Late Palaeozoic Dyamberin beds. Emplacement was apparently by fluidization processes attending exsolution of volatiles from mafic magma at shallow crustal depth. This led to magma fragmentation and incorporation of abundant sedimentary country rock clasts. Post-emplacement hydrothermal alteration of the breccia has been focused on the mafic clasts and matrix, with the development of initial carbonate + sericite (± sulphide) and subsequent imposition of kaolinite ± hematite alteration with crystalline kaolinite in interstices. Weathering has further degraded primary and hydrothermal characteristics. By use of less mobile trace elements, the breccia matrix is inferred to be of nephelinitic composition and unlikely to be affiliated with nearby Late Permian calcalkaline lamprophyre dykes. A link may exist with basanitic lavas in the adjacent Tertiary Doughboy and Ebor volcanic provinces, and with nephelinitic occurrences elsewhere in the New England region. Although there are some similarities with rocks implicated as sources of sapphire and diamond, neither of the latter, or their characteristically associated indicator minerals, have been recognized.
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